function test2
    function filter_output = bfilter(options)
        order = 20;
        filter_output = [];
        for index = 1:2
            b = firpm(order, options.fc, options.data);
            filter_output = [filter_output, filter(b, 1, options.input(:, index))];
            size(filter_output)
        end
    end

    options.data = [
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        0,
        1,
        0,
        0
        ]';
    length(options.data)
    options.fc = [0, 0.025, 0.075, 0.125, 0.175, 0.225, 0.275, 0.325, 0.375, 0.425, 0.475, 0.525, 0.575, 0.625, 0.675, 0.725, 0.775, 0.825, 0.875, 0.925, 0.975, 1];
    length(options.fc)
    options.input = audioread('piano.wav');
    options.fs = 44100;
    [options.len, options.track] = size(options.input);
    
    % filter handler
    y_out = bfilter(options);
    
    soundview(y_out, 44100);
end
